The tap drill for an M16 x 1.5 thread is a 14.5 mm drill (0.5709 in), which leaves about 77% of full thread with a cutting tap. The ideal hole for 75% thread is 14.54 mm, and 14.5 mm is the nearest standard metric drill.
| Percent of thread | Ideal hole | Nearest drill | Drill size | Thread achieved |
|---|---|---|---|---|
| 50% | 15.03 mm | 15 mm | 15.00 mm / 0.5906 in | 51% |
| 60% | 14.83 mm | 15 mm | 15.00 mm / 0.5906 in | 51% |
| 65% | 14.73 mm | 14.5 mm | 14.50 mm / 0.5709 in | 77% |
| 70% | 14.64 mm | 14.5 mm | 14.50 mm / 0.5709 in | 77% |
| 75% | 14.54 mm | 14.5 mm | 14.50 mm / 0.5709 in | 77% |
Drill sizes are coarse relative to this pitch: the two drills either side of the target are 26 points of thread apart. 14.5 mm (0.5709 in) gives 77% and a stronger but harder-to-tap thread; 15 mm (0.5906 in) gives 51% and less tapping torque. On M16 x 1.5 the choice is mostly about tapping torque and machine power.
M16 x 1.5 shows up on hydraulic ports, gland nuts and machine tool spindle hardware. Its basic pitch diameter is 15.03 mm and its tensile stress area is 167.2 mm². A bolt of this size passes through a 17.50 mm normal-fit clearance hole (ISO 273).
Example: M16 x 1.5 at 75% thread
Result: 14.5 mm (0.5709 in), 77% thread
| Major (nominal) diameter | 16.00 mm / 0.6299 in |
|---|---|
| Pitch | 1.5 mm |
| Basic pitch diameter (d − 0.6495·P) | 15.03 mm |
| Basic minor diameter, internal (d − 1.0825·P) | 14.38 mm |
| Tensile stress area | 167.2 mm² |
| Fit | Hole diameter |
|---|---|
| Close | 17.00 mm / 0.6693 in |
| Normal | 17.50 mm / 0.6890 in |
| Loose | 18.50 mm / 0.7283 in |
All Metric fine sizes:
Use 14.5 mm (0.5709 in). It leaves 77% of full thread with a cutting tap; the ideal 75% hole is 14.54 mm. For an easier-to-tap 50% thread, 15 mm (0.5906 in) gives 51%.
14.5 mm is 0.5709 in. The nearest inch drill to the 75% target is 37/64" (0.5781 in), which gives 68% thread.
A forming tap needs a bigger hole: 15.34 mm for 65% thread, so drill 15.5 mm (0.6102 in). Forming taps work in ductile metals such as aluminum and mild steel.
For M16 x 1.5, ISO 273 gives close fit 17.00 mm, normal fit 17.50 mm and loose fit 18.50 mm. The hole depends only on the diameter, so M16 x 2 uses the same sizes.
167.2 mm², from As = π/4 × (d − 0.9382 × P)². Multiply it by the bolt material's proof or tensile strength to get the load the thread can carry.
No. The drill depends on the pitch, not only the diameter. M16 x 1.5 takes 14.5 mm (0.5709 in); M16 x 2 takes 14 mm (0.5512 in). Check the pitch on the drawing before you drill.
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